This invention relates to audio/visual systems and, more particularly, to an improved multipurpose, film handling cassette for sound motion picture systems.
Motion picture systems including a multipurpose film cassette in which a film strip is contained without removal during exposure, processing and projection operations are described in prior U.S. Pat. Nos. 3,615,127, 3,600,071, and 3,895,862. In accordance with the disclosures of these patents, the film cassette is first placed in a camera for exposure of the film strip therein in conventional fashion. After exposure, the cassette is loaded into a viewing device which first subjects the cassette to a sequence of operations during which the film strip is processed to develop a series of image transparency frames. The same viewing device then projects the developed image frames onto a screen for motion picture viewing.
The cassette system represented by the disclosure of these prior patents may be provided with an audio capability as disclosed in prior U.S. Pat. Nos. 3,604,790 and 3,856,387. In the audio/visual systems disclosed in these latter patents, a magnetic sound recording track is provided along one or both of the longitudinal borders of the cassette contained film strip and the cassette includes a provision for moving a loop of the film strip in operative relationship with a transducing head forming part of an audio system. While the arrangements disclosed in these patents provide generally acceptable audio reproduction, the narrow width of the audio tracks necessitated by their being carried directly on the film strip limits the level of sound quality which may be achieved or, conversely, increases the degree of sophistication or cost required of the audio system to achieve high fidelity.
The sound track dimensional limitations of the prior systems may be solved by providing in the cassette a separate audio tape in addition to the usual photographic film strip. Both the tape and the strip may extend between, and may be interwound in nesting convolutions on, cassette contained supply and takeup spools. In this way, both the tape and the film strip may be simultaneously wound or unwound from the respective spools but the path through which the sound tape passes between the spools is different from that of the film strip. In particular, the film strip travels through a path including an exposure/projection station whereas the sound tape travels in a path including an audio transducing head and drive capstan.
The principal difficulty encountered with such dual web systems in the multipurpose cassettes having a provision for processing the motion picture film strip is the tendency for the sound tape to adhere to the emulsion or, at least, to processing fluid on the film strip emulsion during the period just following the deposition of processing fluid on the film strip. This problem may be overcome by providing a mechanical stripping device for separating the sound tape from the film strip. Relative movement of the mechanical stripping device and the film strip, however, is likely to produce an undesirable wearing and possibly damage to one or both webs, particularly after repeated projection cycles.
The film strip currently used in the system is an additive color film structure including, in the order of light transmission during exposure, a transparent polyester carrier base, an additive color screen, a processing fluid barrier layer, a positive image receiving layer or interface, a silver halide emulsion or negative image receiving layer, and an inner layer of antihalation dyes and image stabilizer. When processed by coating the inner layer with a thin uniform layer of processing fluid or liquid, the chemicals contained in the processing fluid permeate the inner layer to the emulsion to develop exposed silver halide grains and render them essentially transparent. Unexposed silver halide grains migrate by diffusion to the positive image-receiving interface at which they are transformed into an opaque silver image in varying degrees of density. During and after development of the images, the antihalation dyes in the inner layer are bleached to become colorless. The negative image in the emulsion is sufficiently low in covering power relative to the positive image that the film strip may be viewed by projection of light in a direction proceeding through the inner layer, the processed emulsion layer and the remaining positive image carrying portions of the film strip and the color screen.
The presence of the spent emulsion layers on the film strip after processing and during projection can be characterized as a compromise between advantages to be gained by removal of these layers and difficulties heretofore experienced in achieving their removal while retaining the desirable characteristics of the present system, particularly those characteristics attributed to the retention at all times of the film strip in the same cassette in which it was initially packaged. A principal advantage to be gained by removing the spent inner emulsion layers is greater transmissibility of the processed film during projection. The problems resulting from retention of the spent inner and emulsion layers on the processed film strip have been recognized previously and dealt with by stripping these layers from the film after processing. See, for example, U.S. Pat. Nos. 3,455,633; 3,709,588, and 3,711,192.